Macroscopic Wigner's friend paradoxes: Consistency with weak macroscopic realism

Wigner's friend paradoxes highlight contradictions between measurements made by friends inside a laboratory and superobservers outside the laboratory, who have access to an entangled state of the measurement apparatus. Where there are two separated laboratories, the contradictions lead to no-go theorems for observer-independent facts, thus challenging concepts of objectivity. Here, we examine the paradoxes from the perspective of establishing consistency with macroscopic realism. We present versions of the Brukner-Wigner's-friend and Frauchiger-Renner paradoxes in which the spin-$1/2$ systems measured by the friends correspond to two macroscopically distinct states. The local unitary operations ${U}_{{\ensuremath{\theta}}_{j}}$ that determine the measurement settings ${\ensuremath{\theta}}_{j}$ at each laboratory are carried out using nonlinear interactions, which are tailored to ensure that measurements need only distinguish between the macroscopically distinct states. The macroscopic paradoxes are perplexing, seemingly suggesting there is no objectivity in a macroscopic limit. However, we demonstrate consistency with a contextual weak form of macroscopic realism (wMR): The premise wMR asserts that each system $j$ can be considered to have a definite spin outcome ${\ensuremath{\lambda}}_{{\ensuremath{\theta}}_{j}}$, at the time after the system has undergone the local unitary rotation ${U}_{{\ensuremath{\theta}}_{j}}$ to prepare it in a suitable measurement basis. We further show that the paradoxical outcomes imply failure of deterministic macroscopic local realism and arise when there are unitary interactions ${U}_{{\ensuremath{\theta}}_{j}}$ occurring due to a change of measurement setting at both laboratories, with respect to the state prepared by each friend. In models which validate wMR, there is a breakdown of a subset of the assumptions that constitute the Bell-locality premise. A similar interpretation involving a contextual weak form of local realism exists for the original paradoxes.